A battery is installed in a vehicle for supplying power to a starter to start an engine. The battery may also be used as a power source for supplying power to various on-vehicle devices. The battery is charged by an electric generator when the engine is running, for example, during driving. In contrast, the battery is not charged when the engine is stopped. A state of charge of the battery decreases if the power is being supplied to the on-vehicle devices or a dark current exists. The state of charge of the battery may decrease to a level at which the engine cannot be started, i.e., the battery may run out.
There is a known technology (for example, JP-A-2006-327487) for shutting down a power supply route for supplying power to an on-vehicle device, which consumes a dark current, when a battery voltage of a vehicle, the engine of which has stopped, reaches a predetermined value.